The present invention comprises a continuously variable transmission (CVT) mechanism. In general, automotive vehicles use manual or automatic transmissions for changing the drive ratio between the engine output shaft and the drive wheels. The transmission is "shifted" or changed in finite steps from start-up, when a high-torque, low speed drive is provided up to highway speeds, where a high-speed, low torque drive is provided. Shifting is accomplished by the driver displacing a shift lever to change the ratio in a manual transmission, or in an automatic transmission by the controlled release and engagement of friction elements. Because the shifting is in step functions, it is manifest that the most efficient operation (fuel consumption, engine efficiency, and so forth) can only be approximated with a transmission which changes gears in discrete steps. It is thus desirable to provide a continuously variable transmission where the gear ratio is varied in a regular, continuous manner, as the vehicle is started and accelerated to driving speeds.
The use of such a CVT employing variable-pitch pulleys in machine tools and similar variable speed systems has been known for some time. Recently considerable work has been directed to the improvement of such a continuously variable transmission to provide a practical component for an automotive drive train. One example of such a CVT is described and shown in U.S. Pat. No. 4,094,203--Van Deursen et al. This arrangement employs a steel belt to transfer drive between the relatively movable sheaves of a primary and secondary pulley. By controlling the sheave displacement--and thus the effective diameter--of each pulley, a considerable range of speed variation is attained in a continuous manner, without the step function change previously noted in connection with manual and automatic transmissions. Even with recent advances, such CVT transmissions for automotive use have still been difficult to manufacture, and imposed weight and volume requirements not unlike those of other transmissions.
It is, therefore, a primary object of the present invention to produce a continuously variable transmission mechanism suitable for automotive use which is simple to manufacture and of a practical size.
It is a more specific object of the invention to produce such a CVT mechanism in which all the drive and control components are mounted on only two axes to simplify manufacturing and installation.